An assessment of intrinsic noise of pseudo-reference electrodes and instrumental noise to enable reliable electrochemical noise measurements in situ on organically coated metal

Electrochemical noise measurement (ENM) is well-established as a standard test procedure for laboratory use to assist in assessing organic coatings. However, its non-destructive nature makes it particularly appealing for field use i.e. the monitoring of actual structures. A fundamental requirement for collecting valid electrochemical noise data in any situation is the use of a stable reference electrode that produces as little noise as possible. This is particularly important for organically coated substrates, where the currents being measured are very small due to attenuation of the signal by the high-impedance coating. Standard electrodes, e.g. the saturated calomel electrode, are not suitable for field measurements. In the present study, a method of assessing candidate electrodes and their noise characteristics is proposed leading to a suggestion for a suitable pseudo-reference electrode (PRE). An important conclusion is that when used as a PRE, the area of the electrode influences the noise characteristics. In general, the smaller the electrode the lower the current noise. But this has to be balanced against small electrodes having higher impedance, the latter being undesirable, so an optimization is needed.